Method for improving the effectiveness of a magnetic field for magnetizing permanent magnets

ABSTRACT

A method for increasing the coercive force of a permanent magnet produced by a given magnetizing field. The magnet is subjected to the magnetizing field with the initial position of the magnet being no greater than an angle theta of + OR - 45* formed between a predetermined direction of magnetization of the magnet and the direction of the applied magnetizing field. The magnet and/or magnetizing field are moved in at least a single plane through the angle theta which can range up to + OR - 45*. Such movement is terminated with the magnet in a position in which its predetermined direction of magnetization is substantially parallel to the direction of the magnetizing field.

United States Patent Becker 1 Feb. 1, 1972 [54] METHOD FOR IMPROVING THEEFFECTIVENESS OF A MAGNETIC FIELD FOR MAGNETIZING PERMANENT MAGNETS [52]US. Cl ..l48/103, 148/108, 252/6251, 252/6263 [51] Int. Cl. .1101!13/00, 1-l01f1/10, 1101f 1/04 [58] Field of Search..148/100,101,103,108,102; 252/6251, 62.63

[56] References Cited UNITED STATES PATENTS 2,482,364 9/1949 Pfleger..l48/l08 X 3,036,008 5/1962 Berge ..252/62.63 X 3,066,355 12/1962Schloemann et a1. ..l48/103 X 3,067,140 12/1962 Davis, Jr. .148/108 UX3,113,927 12/1963 Cochardt ..252/62.5

Wootten ..l48/108 X Jesmont et a1... ....l48/103 X 3,279,959 10/1966Oshima et al. ....148/103 3,424,578 l/1969 Strnat et a1. ..75/2133,428,498 2/1969 Heimke ..148/103 X Primary Examinerl-lyland BizotAssistant Examiner-G. K. White Attorney-Charles '1. Watts, Paul A.Frank, James M. Binkowski, Frank L. Neuhauser, Oscar B. Waddell andJoseph B. Forman [5 7] ABSTRACT A method for increasing the coerciveforce of a permanent magnet produced by a given magnetizing field. Themagnet is subjected to the magnetizing field with the initial positionof the magnet being no greater than an angle 0 of 145 formed between apredetermined direction of magnetization of the magnet and the directionof the applied magnetizing field. The magnet and/or magnetizing fieldare moved in at least a single plane through the angle 0 which can rangeup to 245. Such movement is terminated with the magnet in a position inwhich its predetermined direction of magnetization is substantiallyparallel to the direction of the magnetizing field.

10 Claims, 1 Drawing Figure PAI'ENIEDFEB 1m? 3;639;l82

DIRECTION OF MAGNETIZING FIELD I-zfi x PREDETERIVIINED DIRECTION OF IMAGNETIIZATION OF MAGNET I, 1 1

\ DIRECTION OF MAGNETIZIING FIELD JOSEPH BECKER H/S ATTORNEY METHOD FORIMPROVING THE EFFECTIVENESS OF A MAGNETIC FIELD FOR MAGNETIZINGPERMANENT MAGNETS The present invention relates generally to the art ofmaking permanent magnets and is more particularly concerned with a novelmethod for improving the effectiveness of a magnetic field formagnetizing such magnets.

It is generally recognized that the magnetic properties of permanentmagnet materials can be enhanced by reducing them to powders.Ordinarily, magnets of such powders are prepared by subjecting them to amagnetic field to orient the particles, compressing the powder andsintering the resulting compacts. The magnetic powder can also be bondedin rubber or plastic to produce flexible permanent magnets havingspecial utility in permanent magnet motors, as magnetic latches, and inmany other applications. In some instances, the enhancement of theproperties by particle size reduction is offset to a substantial degreeby the accompanying decrease in magnetic coercive force. Due to thenumerous potential applications of permanent magnets, substantiallyincreasing their coercive force has long been recognized as a desirableobjective by those skilled in the art.

I have found that the value of the magnetic coercive force Pi ofpermanent magnets, especially magnets of cobalt rareearth compounds,shows a pronounced dependence on the magnetizing field H Specifically,magnets formed from permanent magnet material powders, especiallypowders of cobalt rare-earth compounds, exhibit an unusually largedependence of coercive force on the previously applied magnetizingfield. This dependence appears even when the coercive forces have thelow values associated with magnets formed from a large particle sizematerial. To develop their best magnetic properties, therefore, thepermanent magnets need to be magnetized in as strong a field aspossible. The stronger the magnetizing field, however, the greater arethe energy requirements for furnishing such a field. In addition, therate of rise of the coercive force l-l with the magnetizing field H,,,,in some instances, suggests that sufficiently strong magnetic fields arenot presently available to any significant extent to impart the highestcoercive force.

I have further discovered that the effectiveness of a given magneticfield used for magnetizing a permanent magnet to increase its coerciveforce can be very substantially enhanced by causing relative motionbetween the magnetic field and the body being magnetized, such motionbeing critical in both extent and kind.

According to the present invention, the relative motion between themagnetizing field and the permanent magnet can be carried out in anumber of ways. For example, it can be carried out by selective movementof the magnet in the magnetizing field, by selective movement of themagnetizing field along or by selective movement of the magnet and itsmagnetizing field. Since the magnetizing field is usually supplied by alarge magnet secured in place, the preferred embodiment of the presentinvention is the selective movement of the magnet in the magnetizingfield.

' Briefly stated, the preferred embodiment of the present inventioncomprises subjecting the permanent magnet to a magnetizing field. Theinitial position of the magnet in the mag netizing field can vary but itshould be no greater than at an angle of i45, the angle 6 being formedbetween a predetermined direction of magnetization of the magnet and thedirection of the applied magnetizing field. For convenience, the magnetcan be positioned initially with the angle 0 having a value of 0, atwhich position, the predetermined direction of magnetization of themagnet and the direction of the magnetizing field are substantiallyparallel. The permanent magnet is then moved in the magnetizing field inat least a single plane through the angle 0 with such angle ranging upto about :45". The movement of the magnet in the magnetizing field isterminated with the predetermined direction of magnetization of themagnet substantially parallel to the direction of the magnetizing field.

The process of the present invention is operable with permanent magnets.Such magnets may be anisotropic or isotropic. If the magnet isanisotropic, it has a magnetically preferred spacial direction, i.e., aneasy axis of magnetization, and its predetermined direction ofmagnetization as used herein is generally such magnetically preferreddirection. If the magnet is isotropic, its magnetic properties are thesame in all spacial directions, and its predetermined direction ofmagnetization as used herein can be any desired direction.

The accompanying figure illustrates one method of carrying out thepresent invention wherein the magnet was positioned initially with theangle 0 having a value of 0, i.e., the predetermined direction ofmagnetization of the magnet was parallel to the direction of themagnetizing field. As shown by the figure, the magnet was moved in asingle plane through an angle of +0, then 0, and then such movement wasterminated with the angle 0 having a value of 0.

In carrying out the process of the present invention, the magnet shouldnot be moved through an angle 0 greater than :45 because such movementwould tend to cause reversal of the magnetization of those particleswhose magnetic axis initially made an angle of more than 45 with thepredetermined direction of magnetization of the sample. Although theangle 6 can have a value less than 1-45", an angle 6 having a maximumvalue of i45 is preferred since it results in most instances in thehighest increase in coercive force.

In the instant process, the coercive force can be further improved bymovement of the magnet through the angle 0 in a plurality of planes. Forexample, movement of the magnet through an angle 6 of up to :45" throughtwo perpendicular planes successively further increases the coerciveforce signifi cantly. Since the angle 0, in circumscription, defines acone, the maximum coercive force is obtained by successively moving themagnet through a number of different planes with the angle 6 equal to:45 so that all orientations of the magnets particles around the coneare covered.

In the process of the present invention, movement of the magnet in themagnetizing field can be carried out manually or mechanically by anumber of conventional techniques. The

rate of movement of the magnet can vary widely since it is not critical.When the desired movement of the magnet is completed, such movement isterminated with the predetermined direction of magnetization of themagnet substantially parallel to the direction of the magnetizing field.After such magnetization, the coercive force of the magnet is measured.

The particular form of the magnet used in the present process can varywidely and is not critical. The greatest improvcment in properties isusually produced with magnets formed from powders of permanent magnetmaterials. The present process, however, is also operable with permanentmagnet materials in bulk form, i.e., thos-e magnets which have neverbeen reduced to particulate form.

Representative of the permanent magnet materials useful in the presentinvention are cobalt-base permanent magnet materials such as CosY, Co Smand Co M wherein M is cerium-rich misch metal. Additional representativematerials are the magnetically hard ferrite powders. Typical of thesepowders are bariumferrite (BaO'6 Fe 0 strontium ferrite (SrO'6FeO andlead ferrite (PbO'Fe O Alternatively, the present process can be carriedout by moving the permanent magnet in the magnetizing field so that theangle 6 is increased by increments. Specifically, starting with theangle 0 having a value of substantially O, the magnet is moved throughan angle 6 having a value greater than 0 but less than 45, throughsuccessively different planes so that its predetermined direction ofmagnetization describes a cone around the direction of the magnetizingfield H',,,. With each additional movement of the magnet so that a coneis defined, the angle 6 is increased until it equals i45.

In another embodiment of the present process, movement of the magnet ina series of successive planes displaced from each other by a suitableangular increment can be accomplished by rotating the magnet through asuitable angle around the predetermined axis of magnetization at thecompletion of each movement in a single plane through the angle 0.

The present invention is further illustrated by the following examples.

EXAMPLE 1 A cylindrical magnet, about five-sixteenths inch in diameterand three-eighths inch long, was prepared from C0,,Sm

' powder which had a particle size of about 325 mesh. The

powder was pressed while in hexane so that excess fluid leaked out ofthe die during compression. It was compressed lightly in a magneticfield of 8,000 oersteds to orient the particles along their easy axis ofmagnetization. The resulting compact was then further compressed outsidethe magnetic field under a Coercive Force Run Magnetizing Procedure(oersteds) 1 With its easy axis of magnetization aligned with thedirection of the magnetic field, i.e., the position of the angle 6, thetest magnet was magnetized in a magnetic field of 23,600 oersteds toestablish a reference state. lt was then magnetized in the oppositedirectionin a magnetizing field of 15,000 oersteds.

2 The, test magnet was returned to its reference state by magnetizing itin a magnetic field of 23,600 oersteds as in run 1. It was thenmagnetized in the opposite direction in a magnetizing field of 15,000oersteds by moving it in the same plane from its 0 position through anangle 6 of 45 then back through the same plane, through the 0 position,through an angle 8 of -45 and back to 0 position as illustrated in theaccompanying figure.

3 The test magnet was magnetized as in run 1.

4 The entire procedure of run 2 was repeated except that magnetizationof the test magnet in the field of 15,000 oersteds was made by moving itthrough the angle 0 of :45 in two perpendicular planes successively. Thetest magnet was magnetized as in run 1.

6 The entire EHOEEKJ rifriwas repea except that magnetization of thetest magnet in the field of 15,000 oersteds was made by moving themagnet i45 in four planes at 45 to each other.

7 The procedure of run 1 was used except that a magnetizing field of20,000 oersteds was used instead of 15,000 oersteds.

8 The procedure of run 2 was used except that a magnetizing field of20,000 oersteds was used instead of 15.000 oersteds.

9 The procedure of run 4 was used except that a magnetizing field of20,000 oersteds was used instead of 15,000 oersteds.

The procedure of run 6 was used except that a magnetizing field of20,000 oersteds was used instead of 15,000 oersteds.

The procedure of run 1 was used except that a magnetizing field of29,000 oersteds was used instead of 15,000 oersteds.

The procedure of run 6 was used except that a magnetizing field of29,000 oersteds was used instead of 15,000 oersteds,

The above table illustrates the significant increase in coercive forcewhich can be produced in a cobalt rare-earth permanent magnet materialby the method of the present invention. Specifically, runs 2, 4, 6, 9and 10 illustrate the process of the present invention. Run 2illustrates movement of the test magnet in one plane with the angle 0being :45" and shows a significantly higher coercive force than thatproduced in control runs 1 and 3 where the strength of the magnetizingfield was the same but the test magnet was stationary. Runs 4 and 6 showan even higher coercive force than run 2 due to movement of the testmagnet in a greater number of planes. Runs 1 1 and 12 illustrate thatwhen the magnetizing field applied is high enough, the coercive force ofthe test magnet remains unchanged by relative motion between the magnetand the magnetizing field.

The present process is operable, therefore, with any per manent magnetmaterial in the range in which the coercive force depends on themagnetizing field, in which range the effectiveness of a givenmagnetizing field can be enchanced. As a result, permanent magnets withhigh coercive forces are available for much wider use than has beenheretofore practicable since the high energy requirements of largemagnetizing fields are eliminated.

EXAMPLE 2 In this example, a commercial oriented strontium ferritecylindrical magnet about one-half inch in diameter and aboutfive-sixteenths inch long was used. The magnet had been oriented alongits easy axis of magnetization.

After stationary magnetization in a field of 10,000 oersteds, with itseasy axis of magnetization substantially parallel, i.e., aligned withthe direction of the magnetizing field, i.e., with the angle 0 having avalue of 0, the magnet had a coercive force of 3,430 oersteds. It wasthen magnetized in the same field by moving it from its position ofalignment with the direction of the field, i.e., the 0 position of 0,through an angle 0 of :45 in four planes, with each plane at 45 to eachother, and terminating such movement with the easy axis of magnetizationsubstantially parallel with the direction of the magnetizing field.After such magnetization, its coercive force was unchanged indicatingthat the magnetizing field was so high that coercive force no longervaried with relative motion.

In its position of alignment with the field, i.e., with its easy axis ofmagnetization parallel with the direction of the field, the strontiumferrite magnet was then magnetized in the opposite direction in amagnetic field of 5,000 oersteds. After such magnetization, its coerciveforce was determined to be 3,000 oersteds. It was then magnetized in thesame field by moving it from its position of alignment, through an angle0 of EXAMPLE 3 The procedure of this example was the same as that setforth in example 2 except that a commercial oriented barium ferritemagnet was used. The magnet had been oriented along its easy axis ofmagnetization.

After stationary magnetization in a field of 10,000 oersteds with itseasy axis of magnetization substantially parallel, i.e., aligned, withthe direction of the magnetizing field, i.e., with the angle 0 having avalue of 0, the magnet had a coercive force of 2,400 oersteds. It wasthen magnetized in the same fi'eld by moving it from its position ofalignment with the direction of the field through an angle 0 of about:45 in four planes, with each plane at 45 to each other and terminatingsuch movement with the easy axis of magnetization substantially parallelwith the direction of the magnetizing field. After such magnetization,its coercive force was unchanged, indicating that the magnetizing fieldwas so high that coercive force no longer varied with relative motion.

In its position of alignment with the magnetizing field, i.e., with itseasy axis of magnetization parallel with the direction of the field, thebarium ferrite magnet was then magnetized in the opposite direction in amagnetizing field of 5,000 oersteds. After such magnetization, itscoercive force was determined to be 2,130 oersteds. It was thenmagnetized in the same field by moving it from its position of alignmentthrough an angle 6 of about i45 in four planes, with each plane being 45to each other, and terminating such movement with the easy axis ofmagnetization substantially parallel with the direction of themagnetizing field. After such magnetization, the coercive force wasdetermined to be 2,380 oersteds.

What is claimed is:

1. A method for increasing the coercive force of a permanent magnet in agiven magnetizing field which comprises subjecting the magnet to themagnetizing field, the initial position of said magnet in saidmagnetizing field being no greater than an angle 6 of i45, the angle 6being formed between a predetermined direction of magnetization of themagnet and the direction of the applied magnetizing field, causingrelative motion between the magnet and the magnetizing field in at leasta single plane through the angle 6 with said angle 0 rang-- ing up toi45, and ending such movement with the predetermined direction ofmagnetization of the magnet substantially parallel to the direction ofthe magnetizing field.

2. A method for increasing the coercive force of a permanent magnet in agiven magnetizing field which comprises subjecting the magnet to themagnetizing field, the initial position of said magnet in saidmagnetizing fieldbeing no greater than an angle 6 of 1-45, the angle 0being formed between a predetermined direction of magnetization of themagnet and the direction of the applied magnetizing field, moving thepermanent magnet in the magnetizing field in at least a single planethrough the angle 6 with said angle 6 ranging up to about 1-45", andending such movement of the magnet in the magnetizing field with thepredetermined direction of magnetization of the magnet substantiallyparallel to the direction of the magnetizing field.

3. A method according to claim 1 wherein said predetermined direction ofmagnetization is the magnetically preferred direction of magnetization.

d. A method according to claim 2 wherein the initial position of saidmagnet in said magnetizing field is at an angle 0 of substantially 0.

5. A method for increasing the coercive force of a permanent magnet in agiven magnetizing field which comprises subjecting the magnet to themagnetizing field, the initial position of said'magnet in saidmagnetizing field being no greater than an angle 6 of the angle 6 beingformed between a predetermined direction of the magnet and the directionof the applied magnetizing field, moving the permanent magnet in themagnetizing field in a plurality of planes through the angle 6 with saidangle 0 ranging up to about :45, and ending such movement of the magnetin the magnetizing field with the predetermined direction direction ofmagnetization of the magnet substantially parallel to the direction ofthe magnetizing field.

6. A method according to claim ll wherein said permanent magnet materialis a cobalt rare-earth compound.

7. A method according to claim 6 wherein said cobalt rareearth compoundis a member of the group consisting of Co Y, C0,,Sm and Co M wherein Mis cerium-rich misch metal.

8. A method according to claim ll wherein said permanent magnet materialis a magnetically hard ferrite.

9. A method according to claim 8 wherein said magnetically hard ferriteis selected from thegroup consisting of barium ferrite, strontiumferrite and lead ferrite.

10. A method for increasing the coercive force of a permanent magnet ina given magnetizingfield which comprises subjecting the magnet to themagnetizing field, and causing relative angular motion between themagnet and the magnetizing field within an angle 6 of t45 between apredetermined direction of magnetization and the direction of theapplied magnetizing field.

2. A method for increasing the coercive force of a permanent magnet in agiven magnetizing field which comprises subjecting the magnet to themagnetizing field, the initial position of said magnet in saidmagnetizing field being no greater than an angle theta of + or - 45*,the angle theta being formed between a predetermined direction ofmagnetization of the magnet and the direction of the applied magnetizingfield, moving the permanent magnet in the magnetizing field in at leasta single plane through the angle theta with said angle theta ranging upto about + or - 45*, and ending such movement of the magnet in themagnetizing field with the predetermined direction of magnetization ofthe magnet substantially parallel to the direction of the magnetizingfield.
 3. A method according to claim 1 wherein said predetermineddirection of magnetization is the magnetically preferred direction ofmagnetization.
 4. A method according to claim 2 wherein the initialposition of said magnet in said magnetizing field is at an angle thetaof substantially 0*.
 5. A method for increasing the coercive force of apermanent magnet in a given magnetizing field which comprises subjectingthe magnet to the magnetizing field, the initial position of said magnetin said magnetizing field being no greater than an angle theta of + or -45*, the angle theta being formed between a predetermined direction ofthe magnet and the direction of the applied magnetizing field, movingthe permanent magnet in the magnetizing field in a plurality of planesthrough the angle theta with said angle theta ranging up to about + or -45*, and ending such movement of the magnet in the magnetizing fieldwith the predetermined direction direction of magnetization of themagnet substantially parallel to the direction of the magnetizing field.6. A method according to claim 1 wherein said permanent magnet materialis a cobalt rare-earth compound.
 7. A method according to claim 6wherein said cobalt rare-earth compound is a member of the groupconsisting of Co5Y, Co5Sm and Co5M wherein M is cerium-rich misch metal.8. A method according to claim 1 wherein said permanent magnet materialis a magnetically hard ferrite.
 9. A method according to claim 8 whereinsaid magnetically hard ferrite is selected from the group consisting ofbarium ferrite, strontium ferrite and lead ferrite.
 10. A method forincreasing the coercive force of a permanent magnet in a givenmagnetizing field which comprises subjecting the magnet to themagnetizing field, and causing relative angular motion between themagnet and the magnetizing field within an angle theta of + or - 45*between a predetermined direction of magnetization and the direction ofthe applied magnetizing field.